The present invention relates to methods and apparatus for magnetic levitation or suspension of an object, part or magnet at a desired position that is electronically stabilized with Hall effect sensors.
There are many applications for utilizing magnetic levitation to minimize friction, make force measurement, design, and entertaining devices. Friction can be minimized by magnetic levitation for motors, turbines, generators, trains, projectile guns, etc. Magnetic suspension or levitation is an important technique to measure force on an object in a wind tunnel. Wires, cables etc. used to suspend an object in a wind tunnel will interfere with the force measurement. Some fluid density measurements require magnetic suspension to prevent surface tension from interfering with buoy suspension line. High pressure fluid density measurement require magnetic suspension to measure the force on a buoy through the walls of a high pressure vessel. A number of magnetic levitation devices have been built to demonstrate a floating object with no visible support, which spectacular feature is commonly known to the general public via the manufacture of various novelty or entertainment devices.
There are many applications for magnetic levitation that require position sensing and feedback control. Stable magnetic levitation or suspension can be achieved in a totally passive system using a superconductor. However, in some cases it is not possible or practical to use a passive system. Magnetic levitation can be accomplished in an active system using an electromagnet, position sensor, and feedback control circuit. The electromagnet is driven with an electrical current which is used to maintain the levitated object in a stable position at a general location situated beneath the electromagnet. The position sensor detects the position of the levitated object for the feedback circuit. The feedback circuit controls the current in the electromagnet to maintain a given position. Stable magnetic levitation is maintained in the system by increasing the lifting current in the electromagnet when the object falls away from the electromagnet and the lifting current decreases when the levitated object moves up towards the electromagnet. A number of different position sensors are currently used to maintain stable magnetic levitation. The position of a levitated object can be detected optically when a light beam is interrupted and the optical detector changes the current in the lifting coil. In the case of measuring fluid properties or fluid conditions, this limits fluid measurement to optically transparent fluids and vessels, where the range of possible fluid measurements include, but are not limited to, flowrate, density, viscosity, phase change, and phase equilibria properties. A liquid meniscus or droplet can also interfere with the light beam. Inductive and capacitive detectors are also limited by the materials that the fluid containment vessel is made of. Hall effect sensors can detect the position of a permanent magnet in tubes made of metals, ceramics, glass, sapphire, and any material that will allow some detectable magnetic field to penetrate the material. With the recent development of low cost amplified hall effect sensors and power amplifiers this technology is easily adapted to a wide variety of applications.
Accordingly, it is an object of the present invention to provide methods and apparatus for achieving electronically stabilized magnetic suspension of objects, parts or magnets at desired positions using hall effect sensors. It is a further objective of the present invention to provide methods and apparatus for, but not limited to, fluid property measurement, wind tunnel measurements, trains, monorails, transportation equipment, toys, novelty or entertainment devices etc.